The present invention relates to a device for molding a dental shade guide and in particular to a device for molding a shade guide used for determining dental composite resin paste closest to the shade of natural teeth of a dental patient, the shade guide being molded from dental composite resin paste actually used for restoration of the natural teeth. The present invention also relates to a method of molding the shade guide by the molding device.
Recently, in dental restoration when a natural tooth is partially lost in an oral cavity of a dental patient, in order to improve aestheticity of the partially-lost natural tooth to be restored or an artificial tooth substituted for the natural tooth, a number of shade guides are prepared. By comparing the shade guides arranged in order of density with the shade of natural teeth of the patient, the shade guide that match the natural teeth in shade is determined as disclosed in U.S. Pat. No. 5,149,267B1. The photo-curable composite resin paste is prepared based on selected shade guide as disclosed in JP2004-203865A.
Specifically, in order to select the shade of the composite resin paste, as shown in FIG. 5, a shade guide 101 for selecting the shade of composite resin paste comprises a shade guide portion 102 which is compared in shade with the front face of a natural tooth, and a handle 103 integrally molded with the shade guide portion 102 like a rod by a mold (not shown) in Japanese Design No. 1242228.
The shade guides 101 in Japanese Design No. 1242228 are arranged circumferentially of a round plate 105 forming a shade guide holder 104 in order of density.
In the round plate 105, there is a plurality of guide grooves 106 extending radially at regular intervals circumferentially. An inner edge 106a of the guide groove 106 engages in an engagement groove 106a on each side of the handle 103 to make the handle 103 slide radially inward, so that the shade guide 101 is detachably disposed.
On the rear side of a shade guide portion 102 of the shade guide 101, there is a projection 102a which engages in an inner hole of two holes 107 disposed on an extended line of the guide groove 106 of the round plate 105.
In FIG. 5, in the middle on the front side of the handle 103 of the shade guide 101, there is formed a concave finger-contacting portion 103b on which a thumb is applied to allow the shade-guide portion 102 of the shade guide 101 to slide by pressing out of the guide groove 106, so that the projection 102a engages on the outer hole 107.
Thus, the shade-guide portion 102 of the shade guide 101 is kept to project from the outer circumference in FIGS. 6 and 7 thereby preventing dropping the selected shade guide 101 out of the round plate 105 unintentionally.
In FIG. 6, while the patient's mouth opens, the shade guide portion 102 of the shade guide 101 on the outer circumference of the round plate 105 gets close to a natural tooth to be restored or adjacent teeth. While grasping the center of the round plate 105 with one hand, the round plate 105 turns clockwise or counterclockwise with the other hand as shown by an arrow in FIG. 6. By comparing a front side 102a of the shade guide portion 102 in shade with the natural tooth, the shade guide 101 closest to the natural tooth to be restored or adjacent teeth is determined.
The selected shade guide 101 ensures the shade of dental composite resin paste.
The shade guide 101 disposed in the shade guide holder 104 is limited to about ten in number, and colored industrial plastic material is used as the shade guide 101. The adjacent shade guides 101 differ from each other in shade greatly and its texture is poor compared with natural teeth. It is likely to cause difference in shade not only in the shade guide 101 selected by the shade of a natural tooth to be restored but also in composite resin paste selected by the shade guide 101.
Common composite resin is likely to change in shade with a production lot. Before and after curing, its shade is likely to differ slightly. Thus, the composite resin paste selected with the shade guide 101 differs in shade from patient's teeth after restored.
Furthermore, as shown in FIG. 5, the front face of the shade guide portion 102 of the shade guide 101 is tilted so that light is uniformly reflected, while the concave front face of a natural tooth is likely to cause diffused reflection of light. Even if the shade guide 101 is identified in shade with the natural tooth, the cured composite resin determined by the shade could subtly differ from the natural tooth.
In order to produce the shade guide as above, for example, a handle is separately molded and photo-curable paste-like dental composite resin is supplied on the upper end of the handle like a tooth shape. The composite resin is cured by radiating light to form the glossy shade guide 102 close to natural teeth.
However, the shade guide portion has an uneven surface. When light is radiated to the dental composite resin paste filled in a mold to cure the composite resin paste, the surface in an opening of the mold comes in contact with air to form an uncured or unpolymerized layer which has to be removed by grinding to make the surface of the shade guide portion smooth.